Reaction product of thiourea, an aldonic acid and zinc oxide



Patented Oct 21, 1952 REACTION PRODUCT OF THIOUREA, AN ALDONIC ACID AND ZINC OXIDE Allan E. Chester, Highland Park, Ill., assignor to Poor & Company, Chicago, Ill., a corporation of Delaware No Drawing. Application December 6, 1950,

Serial No. 199,582

conate acid which are soluble in acidic aqueous solutions.

Another object of the invention is to provide new compositions of matter which are particularly adapted for use in electroplating baths, especially acid zinc plating baths.

A further object of the invention is to provide a new and improved method for producing compositions of the type described above. Other objects will appear hereinafter.

In accordance with the invention, it has been found that new and useful compositions of matter are obtained by reacting together thiourea, zinc oxide and an aldonic acid, preferably gluconic acid.

The reaction takes place exothermically and the temperatures employed are preferably between 185 F. and 200 F. The preferred procedure is to mix the thiourea with an aqueous solution of the aldonic acid, for example, commercial gluconic acid, and then to add the zinc oxide slowly. When the addition is complete and foaming subsides the reaction mixture is preferably brought to a temperature of 200 F. and maintained at that temperature for about 20 to 30 minutes. The reaction mixture is then cooked at a somewhat lower temperature to a predetermined viscosity from which it will set up as a solid when allowed to cool.

While the compositions of the invention are especially usefulfor the preparation of electroplating baths,' fparticularly acid zinc plating baths, it will be understood that they can be used for other purposes, as for example in the manufacture of skin ointments.

The invention will be illustrated but is not limited by the following examples.

Example I Thiourea, an aqueous solution of 50% gluconic acid and zinc oxide are mixed together in the following amounts:

Pounds Thiourea 9.16 Gluconic acid (50% concentration) 575.00 Zinc oxide (less than 0.1% lead) 63.845

since the reaction takes place exothermically.

When the addition is complete and foaming subsides the batch is brought to a temperature of 200 F. and maintained at this temperature for 20 minutes. While regulating the temperature between 2 185 F. and 195 F. the batch is cooked approximately 2% hours or until the viscosity of 96 ml. (milliliters) of the product is 75-77 seconds. The viscosity determination is made with a 100 ml. pipette No. 715 calibrated to deliver 100 ml. of water in 45 seconds at 20 C.

The reaction mixture is tested at intervals. When the viscosity is seconds or less, 1 hour is allowed between tests. When the viscosity is seconds tests are made every half hour. When the viscosity is 72 seconds tests are made every 20 minutes. At ,65 seconds the pH of a 10% aqueous solution of the reaction mixture should be 6.0 to 6.5. If the pH is below 6.0 more zinc oxide is added to bring it up to the required range. If the pH is above 6.5 more gluconic acid is added. At 75-77 seconds viscosity the reaction mixture is poured into trays in layers of about A to /2 inch thickness. After 24 hours the product is placed on a galvanized screen rack to air dry. When it is dry it is milled to break it up into solid particles of the desired size. The resultant product is readily soluble in acidic aqueous solutions having a pH within the range of 1.5 to 6.0.

Example II This exampl illustrates the application of the invention to the preparation of acid zinc plating baths. The composition prepared as in Example I when added in proportions of l to 3 ounces per gallon to an acid zinc sulfate plating bath containing to 450 grams per liter of zinc sulfate (ZnSO-iflHzO) produces a brightening effect at pI-Is within the range of 1.5 to 6.0. This plating bath will operate near a pH of 6.0 without the formation of zinc or iron precipitates and produces high specular reflectivity of the plated metal going up to mirror brightness, depending upon the quantity of the zinc gluconate-thiourea composition employed. Excellent deposits are obtained over a wide range of current densities from 5 amperes per square foot to 5000 amperes per square foot, the current density employed being dependent upon the agitation available. 1

The compositions of the present invention are especially effective in the electrodeposition of zinc from acidic baths in which the zinc is principally present as zinc sulfate. The zinc sulfate baths can also contain additions of zinc chloride, preferably not more than 20 to 100 grams per liter.

In plating from acid zinc baths containing the compositions herein described it is sometimes desirable to employ a small amount of aluminum sulfate in the bath, for example, to Zounces per gallon. The aluminum sulfate forms a film of colloidal alumina in the vicinity of the anode and prevents excessive acid attack on the zinc crystalline structure of the zinc and have some whitening effect. Still another optional ingredient is sodium fluoride which acts as a whitening and grain refining agent at the cathode and apparently causes more uniform solution of zincat the anode while tending to prevent sludge formation. Other ingredients such as sodium acetate may also be employed but are not required.

Electroplating baths made with compositions of the invention may be used as baths for plating piece-work, that is, for batch operations, or may be employed in continuous plating operations.

If the electroplating baths are used in continuous plating operations the makeup bath may be prepared as described in Example 11 and thereafter the gluconate which is lost due to drag-out is replenished by adding 5 to 100 grams per liter of zinc gluconate at intervals as predetermined by tests of the bath. The zinc gluconate may be prepared as described in Example I by omitting the thiourea. It can also be prepared as described in my copending application Serial No. 180,500, filed August 19, 1950.

The plating baths may be operated at conventional temperatures within the range of 70 F. to 160 F., preferably not higher'than 140 F.

In the preparation of the compositions of the invention other aldonic acids may be used instead of gluconic acid, as for example, mannonic, arabonic, galactonic, and xylonic. The invention contemplates the use of one or more of these acids or mixtures thereof, including mixtures of the lactone forms of these acids. Commercial gluconic acid'is available as a 50% aqueous solution of approximately 99% gluconic acid and 1%- glucose. The delta gamma lactone form of gluconic acid is particularly effective in producing compositions which act' as brighteners'for acid zinc plating baths.

The relative proportions of the reactants employed is subject to variation. For the purpose of the invention it is preferable to determine the proportions, by the pH test given in Example I. The reaction between zinc oxide and gluconic acid to form zinc gluconate requires approximately 1 mole of zinc oxide to 2 moles of gluconic acid but an excess of either reactant may be present in the "final product. The manner in which the thiourea reacts is not clearly understood and the quantities employed may be varied but preferably correspond to 0.025 to 1.0 mole of thiourea per mole of gluconic acid; The preferred molar ratio of thiourea to zinc oxide to aldonic acid is approximately 1:6:12. The molar ratio of thiourea to aldonic acid should be at least 1224' and preferably not more than 1:6. The molar ratio of zinc oxide'to aldonic acid should be at least 1:4 and preferablyabout 1 :2. That the thiourea takes part in the reaction is evidenced by the fact that the same brightening effects cannot be obtained by v adding zinc gluconate and thiourea separatelyto baths ofthe type described.

addition to thexbri'ghtening efiect of the compositions of the invention in acid zinc plating baths, these compositions have a pronounced anti-burn effect. Hence they make it possible to operate the baths at very high current densities with less burning of the plated article.

The term acid zinc sulfate bath is used herein to describe acidic plating'baths in which the zinc is present principally as zinc sulfate but can also be present in minor amounts in one or more other forms.

The invention is hereby claimed as follows:

1.. A method of preparing a composition of 4 matter soluble in acidic zinc sulfate solutions which comprises reacting together thiourea, an aldonic acid and zinc oxide in the presence of water, heating the reaction mixture until a viscosity of approximately '75 to 77 seconds is attained, and drying the resultant product, said viscosity determination being made on a m1. pipette calibrated to pass 100 ml. of water in 45 seconds at 20 C.

2. A method of preparing a composition of matter soluble in acidic zinc sulfate solutions which comprises reacting together thiourea, an aldonic acid and zinc oxide in the presence of water, adjusting the composition of the reaction mixture by adding zinc oxide and the aldonic acid to obtain a pH in a 10% solution of said reaction mixture between 6.0 and 6.5 at a viscosity of 65 seconds, heating the reaction mixture until'a viscosity of approximately 75 to '77 seconds'is attained, and drying the resultant product, said viscosity determinations being made on a 100 ml. pipette calibrated to pass 100 ml. of water in 45 seconds at 20 C.

3. A method of preparing a composition of matter soluble in acidic zinc sulfate solutions which comprises reacting together thiourea, gluconic acid and zinc oxide in the presence of water, heating the reaction mixture until a viscosity of approximately '75 to 77 seconds is attained, and drying the resultant product, said viscosity determination being made on a 100 ml. pipette calibrated to pass 100 ml; of water in 45 seconds at 20 C.

4. A method of preparing a composition of matter soluble in acidic zinc sulfate solutions which comprises reacting together thiourea, gluconic acid and zinc oxide in the presence of water,'adjusting the composition of the reaction mixture by adding zinc oxide and the gluconic acid to obtain a pH in a 10% solution of said reaction mixture between 6.0 and 6.5 at aviscosity'of 65 seconds, heating the reaction mixture until a viscosity'of approximately '75 to 77 seconds is attained, and drying the resultant product, said viscosity determinations being made on a 100 ml. pipette calibrated to pass 100 ml. of water in 45 seconds at 20 C.

5. The product of the reaction of thiourea, an aldonic acid and zinc oxide.

6. The product of the reaction of thiourea, the gluconic acid and zinc oxide.

7. The product of the reaction of thiourea, an aldonic acid and zinc oxide, the molar ratio of thiourea to aldonic acid being within the range of 1:24 to 1:6 and the molar ratio of zinc oxide to aldonic acid being within the range of 1:4 to approximately 1:2.

8. The product of the reaction of thiourea, gluconic acid and zinc oxide, the molar ratio of 'thiourea to gluconic acid being Within the range of 1:24 to 1:6 and the molar ratio of zinc oxide to gluconic acid being within the range of 1:4 to approximately 1:2.

ALLAN E. CHESTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,903,860 Gockel Apr. 18, 1933 2,485,563 Chester et al. Oct. 25, 1949 2,537,032 Chester et al. Jan. 9. 1951 

5. THE PRODUCT OF THE REACTION OF THIOUREA, AN ALDONIC ACID AND ZINC OXIDE. 